1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, it relates to a writing method and apparatus that performs deflection position correction based on a height distribution of a substrate.
2. Description of Related Art
The microlithography technique which advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. In order to form a desired circuit pattern on semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is needed. Thus, the electron beam writing technique, which intrinsically has excellent resolution, is used for producing such a highly precise master pattern.
FIG. 6 is a schematic diagram explaining operations of a variable-shaped electron beam (EB) writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture plate 420, and thereby to irradiate a target workpiece or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g. X direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target workpiece 340 on the stage continuously moving in the X direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shape opening 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) method.
When performing the electron beam writing, there are various factors which generate a position error of the writing apparatus. Deflection error of an electron beam can be cited as one of the factors. Since the writing surface of a substrate is not perfectly even, there are irregularities (concave or convex) on it. Due to height distribution caused by such unevenness, the focal position shifts and the writing dimension also changes. Then, in order to correct, by using a deflection position of the beam, such a writing dimension deviation generated due to the height distribution of the writing surface, there is disclosed a method (e.g., refer to Japanese Unexamined Patent Publication No. 2007-043083) of correcting a deflection position based on the height distribution of the substrate surface, for example. However, with miniaturizing patterns, it is becoming unable to satisfy the requirement of the dimension accuracy if performing only a conventional deflection position correction, because a correction residual error remains for the requirement of dimension accuracy. Therefore, for example, in a multiple writing method, such as a double patterning, it is becoming necessary to suppress a position error to be several nanometers or less, for example.